The disclosure of Japanese Patent Application Nos. 2000-51918 filed on Feb. 28, 2000 and 2000-121590 filed on Apr. 21, 2000 including the specifications, drawings and abstracts are incorporated herein by reference in their entireties.
1. Field of Invention
The invention relates to an internal combustion engine, and more particularly, to an internal combustion engine having a plurality of intake valves or exhaust valves in the same cylinder and capable of controlling valve-opening timing of the intake valves or the exhaust valves, and also relates to a method for controlling the intake valves or the exhaust valves.
2. Description of Related Art
As an internal combustion engine of this kind, Japanese Patent Publication No. 7-111127 discloses an internal combustion engine having a solenoid driving valve mechanism for directly driving an exhaust valve by cooperation of an electromagnetic force of an electromagnet and a spring force of a spring. This solenoid driving valve mechanism biases a shaft body which moves linearly (a lift operation) together with a valve body from opposite sides in its moving direction by means of springs to hold this shaft body together with the moving valve body at a predetermined position (neutral position). The solenoid driving valve mechanism allows the shaft body (valve body) to generate natural vibration, and applies an electromagnetic force to the shaft body from the opposite sides in its moving direction, thereby controlling the motion state of the shaft body and controlling the opening and closing timing and opening amount (lift amount) of each the valve body.
The internal combustion engine having the intake valves or exhaust valves as so-called solenoid driving valves drives and controls individual exhaust valves independently unlike an internal combustion engine of a type (cam type, hereinafter) in which intake valves are opened and closed as camshafts connected to crankshafts through belts are rotated. Therefore, the former internal combustion engine has more excellent characteristics in terms of opening and closing timing (valve timing) of each valve, flexibility in control when the acting angle is changed, and response of valve action when the valve is moved to a desired lift position.
In a solenoid driving valve in which the basic action of a valve body is determined by armature natural vibration generated by spring force of a spring as described above, a displacement speed of the valve body corresponding to a specific amplitude is basically determined by mechanical characteristics (the spring constant) of the spring. On the other hand, in order for the internal combustion engine to obtain an excellent driving state when operating in a wide revolution number region, it is at least necessary to open and close the valve at sufficiently high speed with respect to the high revolution number. As a result, the mechanical characteristics of the spring are usually selected such that the characteristics correspond to the displacement speed of the valve body which can follow the high revolution number.
Furthermore, in the cam type internal combustion engine, since the revolution speed of the camshaft is reduced as the revolution number of the engine is reduced, the opening and closing speed of the exhaust valve is slow in the low revolution number region.
However, in an internal combustion engine having the solenoid driving valve, if the exhaust valve is opened and closed over all revolution number regions at the displacement speed of the valve which is set to be suitable for the high revolution number region of the engine, noise due to exhaust pulsation of the intake and exhaust valves is increased in the low revolution number region of the engine as compared with the cam type internal combustion engine. Although the cycle of exhaust pulsation becomes long as the engine revolution number is reduced, the opening speed of the exhaust valve is not changed as it is. Therefore, as the engine revolution number is reduced, the discharging speed (flow velocity) becomes relatively greater as compared with the cam type internal combustion engine.
Further, in some internal combustion engines, the angle of action of each of the intake and exhaust valves can be varied, and the intake characteristics or exhaust characteristics can be varied by varying the angle of action.
For example, Japanese Patent Application Laid-open No. 8-200025 discloses an internal combustion engine having a plurality of exhaust valves in one cylinder in which the angles of action of the exhaust valves can be varied in accordance with the driving state of the internal combustion engine.
In the internal combustion engine disclosed in Japanese Patent Application Laid-open No. 8-200025, however, the angles of action of the exhaust valves are not continuously variable. Even if the exhaust valves are opened at different valve-opening timings, since there is only one relative offset of the valve-opening timing, it is not possible to arbitrarily set the angles of action of the exhaust valves.
The invention has been made in view of the above circumstances, and it is an object of the invention to provide an internal combustion engine that is capable of appropriately controlling the valve-opening timing of a plurality of intake valves or exhaust valves disposed in one cylinder. In particular, it is an object of the invention to provide an internal combustion engine that is capable of appropriately controlling the relative valve-opening timing between exhaust valves in medium and low engine revolution number regions, and to provide an internal combustion engine capable of setting the angle of action of the intake valves or exhaust valves.
To achieve the above and/or other objects, an internal combustion engine according to a first aspect of the invention includes a plurality of electromagnetically driven exhaust valves in the same cylinder, and a valve-opening timing interval between the exhaust valves is controlled in accordance with the engine revolution number of the internal combustion engine.
In the case of an internal combustion engine, the considerations involved in actuating the exhaust valve differs depending upon the engine revolution number of the engine. For example, in a high revolution number region, the ability to follow (i.e., keep up with) the high speed revolution of the engine output shaft and fast speed for discharging the exhaust gas are required. On the other hand, in a medium and low revolution number region, it is preferable to gently discharge the exhaust gas in order to suppress pulsation of exhaust gas discharged from the combustion chamber. In the case of a solenoid driving valve, because of its mechanical characteristics, it is basically preferable to maintain a constant moving speed of the valve body, i.e., the opening and closing operation speed of the valve body.
According to this aspect of the invention, it is possible to vary the opening speed of the discharge port of exhaust gas without changing the moving speed of each valve body by controlling the interval of valve-opening timing of the exhaust valves. If a case in which the plurality of exhaust valves are opened simultaneously and a case in which the exhaust valves are opened successively with different timings are compared with each other, for example, the discharge port for the exhaust gas can be gently opened in the latter case.
Further, a difference in timing between an exhaust valve having the fastest valve-opening timing and an exhaust valve having the slowest valve-opening timing may be set to increase as the engine revolution number of the internal combustion engine becomes smaller (i.e., decreases).
In the medium and low revolution region, it is preferable to gently discharge the exhaust gas from the combustion chamber in order to suppress the exhaust pulsation.
According to this aspect of the invention, as the engine revolution number becomes smaller, the exhaust gas is discharged more gently, and the exhaust pulsation is suitably restrained. Therefore, the quietness of the engine especially in the low and medium revolution regions is improved.
When the engine revolution number of the internal combustion engine is equal to or smaller than a predetermined revolution number, the relative valve-opening timing of the exhaust valves may be different.
According to this aspect also, the exhaust pulsation is suitably restrained, and the quietness of the engine especially in the same region is improved.
An internal combustion engine according to a second aspect of the invention determines a target angle of action of a plurality of valves provided in the same cylinder, controls the valve-opening timing interval of the valves provided in the same cylinder, and controls the angle of action of the valves to the target angle of action by controlling the valve-opening timing interval of the individual valves.
In this internal combustion engine, two valves are opened and closed with different valve-opening timings. In this case, the effective valve-opening period for that combustion chamber (cylinder) is a period from an instant when one valve which opened first starts opening to an instant when the other valve which opened later finishes closing. This enables the angle of action to be freely set and controlled. Therefore, the flexibility in design of the angle of action of the valve can be enhanced.
In the internal combustion engine of an aspect of the invention, a relative delay amount of the valve-opening timing of the valves for a cylinder may be obtained based on the determined target angle of action, and the interval of the valve-opening timing of the two driving valves may be controlled according to that delay amount.
In the internal combustion engine of an aspect of the invention, only when the target angle of action is smaller than a predetermined value, the valve-opening timing interval of the valves may be controlled so as to differ.
In the internal combustion engine of an aspect of the invention, the plurality of driving valves whose valve-opening timing is controlled can be controlled such that the valve operations thereof are shifted to the valve-closing operation immediately before the valves reach the fully open positions. With this structure, a small angle of action which could not be conventionally set can also be set as the angle of action.
The invention is not limited to the above-described internal combustion engine. The invention applies to a vehicle in which the internal combustion engine of the invention is mounted, and to a method for controlling the valve-opening timing of valves provided in the internal combustion engine.